In the laying of pipe underground such as in the laying of sewer lines, it is necessary to bore and lay the pipe casing underground at a desired percent of grade. It thus becomes necessary to monitor and control the grade of the casing as the bore is cut and the casing is simultaneously pushed through the underground bore to maintain the desired percent of grade. However, the bore and casing cannot be seen as it is formed through extended links underground and the problem of monitoring and maintaining the desired percent of grade is a problem to which considerable attention must be given in order to avoid re-boring.
Heretofore, remote hydraulic grade indicators have been utilized, such as shown in U.S. Pat. No. 3,851,716, which include a sight tube on an indicator board at a boring station connected to a water line which is affixed to the top of the casing being bored and pushed through the ground. Any deviation in the leading edge of the casing from the desired grade either up or down provides a corresponding response to the water level in the sight tube located in the boring pit. Based on the reading of the sight tube, the operator in the boring pit may pivot the head of the casing which carries a cutting head by means of a mechanical linkage. However, the problem arises that the water line connected to the sight tube must be vented on both ends and if the apparatus is utilized below the water table, water can enter the tube and interfere with the reading at the sight tube. The apparatus also has inherent vibration problems which necessitate that the apparatus be shut down to take a reading of the sight tube. The sight tube cannot be monitored simultaneously with the boring operation. With the vibrations, air locks are often created which interfere with the accuracy of the reading in the sight tube. The above inaccuracies can result in the final line being off grade often requiring re-boring. The range of this apparatus is also limited since it reaches its practical limits owing to the mechanical nature of the system. Due to the pivotable connection of the casing head utilized to steer the casing up and down, there is an open space between the casing head and the casing pipe being laid. This space creates a problem if the apparatus is utilized in soft or sandy soil whereby the soil feeds in through the space resulting in cave-in.
An attempt to improve the steering of the above type casing head is disclosed in U.S. Pat. No. 3,939,926 wherein hydraulic actuated wedge mechanisms carried in side openings are utilized to bear against the surrounding earth and provide a steering force. However, this requires considerable complication in the casing head structure and controls therefor. The mechanisms are carried interiorally of the casing head which obstructs flow of the drillings rearwardly from the cutting head.
It has been known to provide a leveling device which utilizes light transmitted through a gravity indicating bubble in a liquid to photoresponsive elements which monitors level conditions such as the spirit level vial shown in U.S. Pat. No. 3,324,564. However, the purposes and problems to which this type of device is directed are not analogous to those herein and such a device would not accurately monitor off-level conditions. The device is also intended for operation in stable environments and would not be suited for use under the dynamic forces of mechanical vibrations owing to the need of maintaining the location of the gravity indicating bubble accurately.
Accordingly, an important object of the present invention is to provide a grade monitor for accurately monitoring the grade of pipe casing being bored and pushed underground.
Still another important object of the present invention is to provide a grade monitor for monitoring the grade of associated mechanical equipment and machinery which is highly accurate and not susceptible to vibrations.
Still another important object of the present invention is to provide grade monitoring and steering apparatus which accurately senses deviations in the percent of grade of casing being bored and laid and changes the direction of the cutting head accordingly in a highly responsive manner.
Yet another important object of the present invention is to provide a slope sensor whose output varies linearly with deviations in percent of grade whereby horizontal bores and lines may be formed true to grade within tolerances of plus or minus one-eighth (1/8") of an inch.
Yet another important object of the present invention is to provide a non-mechanical, solid-state grade monitoring device which can be utilized to monitor and control percent of grade on trenching machinery, motor graders, construction lasers, and other like machinery to obtain a desired percent of grade.